The present invention relates polyimide surfaces. Specifically, the present invention relates to a method of treating a polyimide surface, to treated polyimide surfaces as well as to items manufactured with treated polyimide surfaces.
Polyimide is a kind of condensation polymer derived from bifunctional carboxylic acid anhydrides and primary diamines. Polyimide demonstrates excellent dielectric, thermal and mechanical properties, making it a very good circuit substrate in the microelectronic industry. In the manufacturing of inkjet cartridges, KAPTON (trademark of DuPont for polyimide products) is often used at flex-joint interfaces. Here, proper adhesion between on the one hand polyimide surfaces and on the other hand structural adhesives, encapsulants and/or barrier layers is indispensable for proper and sustained functioning of the inkjet cartridge. Loss of adhesion in such interfaces may cause delamination, ultimately leading to ink-leakage and/or electrical shorts. In fact, failures due to KAPTON/encapsulant and KAPTON/structure adhesive delamination represent the main causes of malfunction for some families of inkjet cartridges.
Up to now, existing methods for improving polyimide adhesion primarily involved chemical modification of a polyimide surface, and can be roughly categorized as dry or wet methods.
Plasma treatment represents the most common dry method of modifying the polyimide surface. Typical plasma treatment methods use plasma to effect chemical change on the polyimide surface. Here, the goal is to positively affect the nature of the surface (such as the surface wetability) without deleteriously modifying the bulk properties of the inner polyimide material. Plasma treatment methods are, however, typically fraught with a major disadvantage, namely the poor long-term stability of the plasma-activated polyimide surface. Extended storage times, contact with humidity as well as elevated temperatures very rapidly attenuate the beneficial effect of plasma on polyimide surfaces, severely limiting the practical usage of this technique.
Wet methods for modification of polyimide surfaces typically involve the use of alkaline reagents. These methods exploit the ring-opening reaction between alkaline and the imide ring of the polyimide. Potassium hydroxide and other similar reagents such as sodium hydroxide or ammonium hydroxide are most commonly used in modifying polyimide surfaces. Treatment with alkaline solution followed by rinsing with acid converts the polyimide surfaces into polyamic acids. Polyamic acids convert back to amorphous polyimide at lower temperatures (150-250xc2x0 C.) and, at higher temperatures (350-400xc2x0 C.), to crystallized polyimide. Disadvantages associated with wet modification methods of this type include the following:
(a) the manufacturing process is complicated by the use of corrosive bases and acids;
(b) incomplete cleaning of the surface following base and/or acid treatment leads to undesired residual impurities which contaminate the surface;
(c) the use of strong bases and acids may also corrode metal traces and change the physical dimensions of desirable fine architectures on the surface.
Several methods have been proposed in the prior art as ways of alleviating problems such as those above.
In U.S. Pat. No. 5,543,493 issued Aug. 6, 1999 for xe2x80x9cMethod For Treating A Polyimide Surfacexe2x80x9d assigned to Samsung Electronics Co., Ltd., a polyimide surface is chemically treated with aliphatic, aromatic or siloxane amines and is then dried. Such treatment was found to increase the adhesion strength between a polyimide surface treated in this way and adhesive.
A further mode of modification is described in xe2x80x9cAdhesion improvement of epoxy resin/polyimide joints by amine treatment of polyimide surfacexe2x80x9d, H. K. Yun et al., Polymer Vol. 38 No. 4, pp. 827-834, 1997. This article describes the modification of polyimide surfaces to improve adhesion strength by immersing polyimide materials in amine solutions and then drying the thusly treated polyimide materials. Here, the adhesion strength was found to increase with increasing molecular weight of the amine used for treatment. Higher molecular weight of the amine used for treatment was also found to require higher subsequent drying temperatures, so that higher adhesion strengths were generally found to necessitate higher drying temperatures.
In light of the importance as described above of polyimide surface adhesion propensity, it is therefore a goal of the present invention to improve this adhesion propensity.
This goal is met by provision of a method for treating the surface of a polyimide as set out in claim 1. In a method for treating polyimide surfaces, a solution containing a pentane functionalized with more than one amino moiety is applied to a polyimide surface. Following this application, the polyimide surface to which the solution has been applied is then dried at a temperature of between approximately 20xc2x0 C. and approximately 120xc2x0 C.
An advantage of the method according to the invention is that improved polyimide adhesion is effected while avoiding less rigorous conditions than usually required by related methods for the modification of polyimide surfaces. For example, according to the inventive method, drying the polyimide surface treated with amine at temperatures as low as ambient (i.e. xe2x80x9croomxe2x80x9d) temperature (defined within the scope of the present invention as approximately 20xc2x0 C.) following treatment of the polyimide surface with the pentane amine is sufficient to engender the desired adhesion enhancement.
That the drying step of the polyimide surface following treatment of the polyimide surface with the pentane amine can be performed at as low as ambient temperature renders the inventive method highly economical, as costly heating elements and power consumption associated therewith are avoided in the treatment process.
A major advantage of the method according to the invention is that polyimide surfaces modified according thereto demonstrate a vast improvement in adhesion propensity to a variety of materials, for example structural adhesives, encapsulants and barrier layer materials, under highly humid adhesion conditions. This is important because the conditions which prevail, for example, in an inkjet cartridge with liquid (i.e. water-based) ink storage fall into this category of humid adhesion conditions. This means that polyimide surfaces modified according to the method of the invention are especially amendable to adhesion to structural adhesives, encapsulants and/or barrier layer materials of inkjet cartridges and are therefore very well suited to use in the construction of such inkjet cartridges.
The goal of the invention is also met by provision of a method for treating a surface of a polyimide as set out in claim 16. In a method of treating a surface of a polyimide according to the invention, a solution containing an aliphatic amine functionalized with more than one amine moiety is sprayed onto a polyimide surface. The polyimide surface to which the solution has been sprayed is then dried.
As described above for the method for treating a surface of a polyimide according to claim 1, the method for treating a surface of a polyimide according to claim 16 benefits from the fact that both the spraying as well as the drying processes can be carried out at ambient temperature, thereby simplifying construction and procedural aspects of polyimide modification. That the solution containing the multifunctionalized aliphatic amine is sprayed onto the polyimide surface to be treated means that costly and cumbersome baths for immersion (the common method of application) can be dispensed with in favor of nozzles which are generally easier to operate, control and maintain.
According to one embodiment of the inventive method, polyimide films, for example KAPTON-films, can be dipped into solutions of pentane amine. Such solutions are preferably in water, an alcohol containing 1 to 4 carbons, or combinations thereof and preferably contain 0.1-0.5% vol/vol percent of pentane amine. Here, the temperature can be ambient temperature, say approximately 20xc2x0 C., however, elevated immersion temperatures of up to approximately 80xc2x0 C. also yield advantageous results. Immersion of the polyimide film into the above solution generally takes place for 5-30 minutes, and drying of the thusly treated polyimide film follows for about an hour at temperatures ranging from ambient temperature up to approximately 120xc2x0 C.
For the case that the amine solution is to be in pure alcohol containing 1 to 4 carbons or in a mixture of this alcohol with water, the inventors have found that the alcohol containing 1 to 4 carbons advantageously contains 3 carbons, i.e. it is propanol. Preferably, the propanol used is isopropanol. For the case that the amine solution is in a mixture of isopropanol and water as the solvent system, it is preferable to use a 1:1 vol/vol mixture of these two components.
It should be emphasized here that the immersion as well as the drying of the polyimide film can be carried out at ambient temperatures while not sacrificing the resulting adhesion strength, thereby simplifying the treatment method as a whole.
In a preferred embodiment of the method according to the invention, pentane amine-containing solutions can be applied onto the polyimide film by spraying. Spraying can take place at temperatures ranging from ambient temperature, say approximately 20xc2x0 C., up to approximately 80xc2x0 C. Drying of the thusly treated polyimide films subsequently takes place as previously described above for immersion-treated polyimide films. Here, as above, it should be emphasized that both the application as well as the drying steps can be carried out at temperatures as low as ambient temperature, thereby greatly simplifying the method as a whole.
It should also be emphasized that in each of the two embodiments described above, positive results can be achieved using solutions of pentane amine containing as little as approximately 0.1% vol/vol of pentane amine. Such low concentrations of pentane amine allow the conservation of process material, thereby implying a further savings in processing cost.
Pentane amines used to functionalize polyimide surfaces according to the method of the invention are preferably pentane diamines of the general formula x,y-diaminopentane, wherein x and y each range independently and integrally from 1 to 5, inclusively. Especially preferred is the use of 1,5-diaminopentane. The inventors have found that the latter compound yields highly advantageous results with respect to the adhesion propensity of the polyimide film following completion of treatment.
According to a preferred embodiment of the method according to the invention in which the amine-containing solution is sprayed onto the polyimide surface, the aliphatic amine used is preferably an aliphatic diamine, an aliphatic triamine or an aliphatic pentamine. Of each of these, 1,5-diaminopentylamine, diethylenetriamine and tetraethylenepentamine, respectively, are especially preferred. Other conditions such as those of solvent system, treatment temperature and drying temperature are as outlined above for preferred embodiments.